Nearly two-thirds of US women of childbearing age are overweight or obese and nearly half, once pregnant, have excessive gestational weight gain (GWG). Excessive GWG is a significant predictor of poor obstetric outcomes and lifelong health risks for a woman and her infant. Obesity, which oftentimes worsens with each pregnancy and advancing age, increases obstetric and fetal complications. Inadequate GWG also poses risks to the mother and infant. African American (AA) women's rates of preexisting obesity and both excessive and inadequate GWG is higher than rates for women of other races, across nearly all BMI categories. Currently, the biobehavioral factors associated with excessive and inadequate GWG are poorly understood, yet in order to improve outcomes, are essential to identify, particularly for AA women. In the proposed pilot study, we will test the hypothesis that an underlying mechanism that contributes to within-race variability in GWG patterns is the structure and dynamics of the gut microbiome during pregnancy and, further, that the brain-gut axis is influenced by biobehavioral factors identified as important contributors to GWG. Increasing evidence supports that the gut microbiome greatly influences the bidirectional signaling between the gastrointestinal tract and the brain. Little is known about the intra-racial variations in the ut microbiome and the brain-gut axis. Even less is known about the gut microbiome across BMI categories, microbiome changes in pregnancy, and maternal behavior profiles linked with GWG. In the parent study, pregnant AA women are recruited among 18 to 35 year-old women during the 1st and 2nd trimesters. For the proposed sub-study an additional 3rd trimester prenatal encounter will be added for a subset of 80 women. This visit will occur between 35-41 weeks' gestation and will involve a 3rd rectal swab and completion of questionnaires on stress, mood, and diet. Nearly all data used in the sub-study will be from the 1st and 3rd trimester data collections. Upon analysis, a two-sample t-test or ANOVA will be used to compare the logarithm transformations of microbes. To compare the percentage of microbes within the same women from 1st to 3rd trimester time points, a paired t-test will be performed on the logarithm transformed percentages. For a more detailed trend analysis over the time points, a mixed effects ANOVA will be performed. Partial correlation analyses will be used to test for pairwise linear associations between the outcomes and interval and/or total GWG after adjusting for the biological and/or psychosocial factors. With the parent study underway, a strong research team is actively investigating the role of the microbiome in AA women's obstetric outcomes, particularly preterm birth. Ms. Edwards, the PI of this proposed study, is gaining vital experience and is poised to begin collecting data and analyzing results. As obesity and improper GWG are known contributors to racial disparities in birth outcomes and chronic conditions, the proposed study will serve as a step toward ameliorating health disparities in AA families.